Refrigerator control



Dec. 7, 1943.

T. s. SAPI-'ORD REFRIGERATOR CONTROL Filed July s, 1942 M Ww ww f u .m M

Patented Dee. "7.,` 1943A UNITED STATES PATENT OFFICE REFRIGERATQRooN'rRoL l Truman Si Salford., Greenwich, Conn. Application July. 6,1342, Serial No. 449,966'

(ci. iz-lis) 3 Claims.

This invention relates to the defrosting of refrigerators of themechanical type in which the heat required for the vaporization of arefrigerant is taken from the articles to be cooled and is moreparticularly concerned with the automatic control of defrostingoperations.

Since the introduction many years ago of artificial refrigeration, Atheaccumulation ofv frost4 'upon the refrigerating surfaces has presentedone of the most annoying andever present problems. Numerous methods ofdefrosting by heat- A ing or dissolving the frost have been suggestedand to some extent have been used, but such methods have been manuallycontrolled and have been dependent therefore upon the care andwatchfulness of the operator. "In domestic refrigerators the coolingunit is often hidden be hind an enameled iron screen, and the operator,often a domestic servant understanding little or nothing of theoperation of the refrigerator, may

before the defrosting is carried out.

"This application includes subject matter common to application SerialNumber 104,840, led

October. 9, v1936, which matured into Patentl 2,319,349, granted Mayv18,1943. `In general, the

apparatus of that invention involves means for automaticallyde-energizing the refrigeratingv vvenient tothe user of therefrigerator. This invention is concerned with an alternative method ofsolving the saine problem in which the delay in the operation of thede-energizing means. `is responsive. to use ofthe refrigerator so thatdefrosting does not takefplace during normal use when refrigerationisrequired but may, and

does, take place if the refrigerator is not opened for a substantialperiod of time.

It is, therefore, an object ofthis invention to.

provide an-autom'atlc defrostingcontrol which will require no attentionon the part of the re-. frigerator user and which will insure thethorough and frequent elimination of frost whileV minimizing thelikelihood of (failure to provide adequate refrigeration at times whenit'is needed for any purpose. 'A i Other objects and advantages of thisinvention vwill be apparent| upon a consideration of the followingdetailed description of a; preferred em bcadiment thereof. inconnectionfwith the annexed drawing wherein: y. Figure'l is a.perspective View of a domestic refrigerator. of the type in whichthe'vaporization v of a liquid. medium is responsible for the coolingeffect, showing various controls arranged according to this invention;

Figure '.2 is a -circuit diagram illustrating the operation of theseveral thermalv switches responsible for deferred vautomatic defrostingof the 4evaporatoncoils of the refrigerator shown in 'lation of onev ofthe thermal switches included Y' cubes or other material to be frozenwithin the allow the frost to collect for weeks or even months Figure 3is a View showing in detail the instalin thev circuit diagram of Figure2. I

The refrigerator box shown in Figure 1 con sists of the usual heatinsulated walls I0, a close tting door' I I, and evaporator unit I2disposed about a tier of drawers adapted to contain ice refrigerator. Inthe preferred form of this invention, to be described in detail in thisapplication,

`evaporator'IZ will be considered as a part of a compressor-expandercircuit in which the compressor is electrically operated by a motor. Itwill be-evident, however, that the present invention is adaptable tovarious types of mechanical and heat-operated refrigerators and that thepresent description is exemplary rather than restrictive in nature. vReferring now to Figure 2, it can be seen that a motor I3 is connectedby conductors I4 and I5 with main'power lines`l6 and I1, respectively.Motor I3 is intendedfor the operation of a compressor to supplyrefrigerant under pressure, the

'latent heat of vaporization of such refrigerant being withdrawnfrom-the articles within insulated box I0 thereby cooling the sa e. Asis customary, vaporization of the refrige ant occurs in evaporator I2.In conductor I4 leading to compressor motor I3 there is disposed athermal switch I8 may be of .that type, iffdesired. .The-

' in form except Afor the disposition of a normally or vapor pressureresponsive switch i I8' of con'- ventional form. This switch is disposedin some position within the insulated box I0 which will 4controltheaverage box temperature. Normally a'swi'tcli of the type of switch I8will be somewhat removed from the evaporator I2 butin a position to`maintain an average temperature of .anydesired. value on those'Ishelves of the 'refrigerator on which objects are stored forrefrigeration. It is contemplated that switch `I8 be entirely con'-ventionalin form. Normally, such switches are capable of adjustment anditis understood that lconductor vI5 connecting the other pole of motorI3 `with the power source is also conventional closed, the operation ofthe refrigerator illustrated is entirely conventional. Under theseconditions, when the temperature falls below a predetermined value,switch I8 opens and allows the refrigerator to warm. An appreciable risein temperature results in the closing of switch I3 and the initiation ofoperation of compressor motor I3 bringing about further refrigeration.

It has been stated that it is an object of this invention to provide acontrol of a type which will cause automatic defrosting at times when itwill be convenient from a standpoint of the refrigerator user. To thisend, the opening of normally closed switch I9 is effected automaticallythrough a control circuit including a relay 20. One pole of relay 20 isconnected by conductor 2I to main line conductor I1, while the otherpole thereof is connected by a conductor 22 to a thermal switch 23 whichis in turn con-v nected through a conductor 24 to another thermal switch25 connected by a conductor 26 to the other main power line I6. Thedisposition and function of thermal switches 23 and 25 forms animportant part of the present invention.

Upon reference to Figure l,"it can be seen that thermal switch 25 isdisposed on orv close to the evaporator I2. This switch is normallyclosed when the evaporator temperature is substantially at or below thefreezing point of water. In other words, the tendency of switch 25-isyto close the cuit opening position.

circuit leading to relay 20 to thereby hold switch I9 open andde-energize motor I3. When, however, the temperature at the evaporatorhas risen to a value consistent with the melting of the frost thereon,for example about 34 'or 35 F., thermal switch 25 will open thusdeg-energizing relay 20 and allowing switch I9 to close thereby causingoperation of motor I3. Switch 25 is of the type commonly known as aterminate defrost. Once open, it does not reclose until a lowtemperature is reached near the minimum of normal operation.

Thermal switch 23, which is also in the circuit controlling theoperation of switch I9, is of the differential type. Such a switch ismanufactured by the Minneapolis Honeywell Regulator Company anddesignated in their catalog as type' L480 in sectionV4-G, form No.95-1244. A thermal switch of this type may be normally disposed incircuit opening position when the temperature responsive portion thereofis exposed to a temperature above a certain value. Upon reduction.

in temperature to said value the switch will move to circuit closingposition but will remain in that position for a differential which maybe as great as a 12 rise in temperature before return to its rst orcircuit opening position. It is-contemplated that thermal switch 23include a capsule 21 held within the interior of the food storagechamber of the refrigerator by a clip 28. Capillary tubing 29 connectscapsule 21 with the switch box 30 which may be disposed on the exteriorof the refrigerator for convenient adjustment.

The location of capsule 21 forms an important part of this invention.Upon reference to Figure 1 it may be seen that said capsule is disposedlon the interior of a wall I0 adjacent the latch side of door II. Inthis position, capsule 21 is mostV exposed to warm air upon the openingof door II and will be exposed also to the warmth of any foods, drinks,and dishes placed on the shelves in the box. It is also evidentl thatbecause of the position Yof capsule 21 itv will be much more affectedbythe opening of the-door I I andby the placement of warm objects in therefrigerator V than will thermal switch I8 which controlsl the Justed tomaintain an average temperature of' 45 F. while thermal switch 25 opensat about 35 and recloses at a temperature aboutA 20". F. Under suchcircumstances, thermal switch 23 can be adjusted to maintain the controlcircuit open at all temperatures above 45 F. but to move to circuitclosing position upon reduction in temperature to substantially 45 F.The differential may be set for 5 or 6 so that switch 23 will stay incircuit closing position until a temperature in the neighborhood of 51is reached.

With the above adjustments of the thermostats, normal use of a householdrefrigerator incidental to the preparation of 3 meals a day includingfrequent opening of the door and placement of warm objects within therefrigerator will keepl thermal switch 23 for the entire day in cir-Under such conditions the relay 20 is de-energized, switch I9 i'sclosed,

. and the refrigerator control is effected in the ation of thermalswitch I8. When this temperature value exists in the vicinity of capsule21 switch 23 will move to circuit closing position.

Since switch 25 is already closed, relay20 will be energized and switchI9 will be opened causing motor I3 to stop. The temperature within therefrigerator will thengradually rise until melting at evaporator I2yraises the temperature at thermal switch 25 to 35. At this time thecontrol circuit will be opened, switch I9 will be closed, and motor I3will resume operation. This will presently cause switch 25 to, closeagain Vand the refrigerator will repeat a defrosting cycle. Eventuallythe temperature at capsule 21 V may reach about 51 .and that switch willreturn to circuitv opening position. Of course, if the refrigerator isused before that time, switch 23 will be immediately. restored tocircuit opening position and normal refrigeration will commence.

From the foregoing it can be seen that before defrosting can occur theremust be a time interval sufficient to permit capsule 21 to be cooled toa temperature determined by adjustment of switch I8. This time intervalhas been found to be sufficiently. great so that it will not occur whena refrigerator is used every 3 or 4 hours as is common in the ordinaryhousehold. However, when no meals are prepared switch 23 may besufficiently cooled to move to circuit closing posipurpose ofillustrating it and instructing others a,sss,so7' in the principlesthereof as well as the best Y practical manner of utilizing theinvention in order that others may be enabled to modify it and apply itin numerous forms each as may be best suited as to conditions andrequirements in templated -that my invention may be appliedto gas andother heat-operated refrigerators, in which case the motor I3 mayoperate a fuel valve or relay tocontrol theenergy supply, instead ofdriving the usual mechanical refrigerator.

What is claimed is:-

1. 'A refrigerator-comprising a cabinet having an insulated chambertherein, refrigerating apparatusincluding. a cooling unit disposedW insaid insulated chambenan element at a'point within the insulated chamberremote from the access opening thereof for controlling the appa- 'ratusfor restricting variations in'temperature frosting ofthe cooling unit,said control means A including a temperature responsive element disposedin said chamber adjacent to the access opening thereof and at a pointremoved from 'the location of the first named element'and in a positionto be effected lto an appreciable 'extent by heat from warm objects.introduced through any particular instance. Inparticular it isconvicinity of thetemperature responsive element reaches the low limit'of a, predetermined teml perature range and suspending operation of thev peratures above the freezing point of ,water to permit therefrigerating apparatus'fto be opera.-

`tive.

3. A refrigerator, according. to claim 1, in which the refrigeratingapparatus includes a motor circuit having a normally clotr .d .switchtherein, and said control means includes a second circuit comprising asolenoid which upon energization of said second circuit opens the switchin the motor circuit. v

1 TRUMAN 8. SAFFQRD.

'said opening into said chamber, said temperature responsive elementbeing of the diiIerential type' and initiating and then permittingoperation of the control means-after the temperaturein the

